Positive or Negative pump? Help needed!

[SuperDario]

Hi all,

We have a flat with 2 showers and 4 wash basins. We have mains supplied cold water and a hot water cylinder located in an airing cupboard along with the boiler. We currently have a Salamander CT Force 30PS which has been playing up, giving intermittent hot water with normal pressure then no pressure as well as a screeching noise coming from the pump. I have been getting conflicting advise on whether their is an issue with the pump/air in the system or whether we can the wrong pump and need the negative Salamander CT Force 30SU.

Any advise would be helpful!

Thanks,
SD

 

[Best]

Does sound like you have air being dragged into pump, or blockage at filters.
Get any filters checked and make sure the pump is piped exactly
to manufacturers instructions.
Ask the installer to come back and sort it, - or did you install it yourself?
If the pump starts no problem when a shower valve or tap is opened, then you don't need a negative head pump.
The pump really should be ideally at base of cylinder and piped so to avoid air.
Could you post some photos of the pump and pipework?

 

[macackau]

Is there a flange fitted to the draw off from the hot water cylinder to the pump?

 

[ShaunCorbs]

i know this wont help you solve your issue but i wouldnt of went down the unvented cylinder route instead of installing a pump esp with two showers

 

[SuperDario]

Thanks for your responses guys. We've checked the filters and ensured the pump has been installed correctly, but the problem has still not been resolved. It is baffling. What we are finding now is that the water is fine in the evenings with only a few seconds delay before the pump starts and the hot water comes out, whereas in the mornings it can take up to 15 minutes for the pump to fire and the hot water to come out of any of the showers or taps.

Any ideas?

 

[chris watkins]

It is never going to work properly with a Positive Head pump which relies on water flow to start it, connected to showers or mixer taps were the hot water has got to overcome the mains cold water.

It still sounds like it is a build-up of air over night which is reducing the flow so it is not starting.

Who spec'ed & installed this booster pump?

First thing in the morning open just the hot tap NO cold at all & come back & tell us if it is still the same.

 

[SuperDario]

Hi Chris, the system was spec'd and installed when we had the flat refurbished last year June. I'm really regretting not going the Megaflow route.

We've put only the mixer tap on hot water this morning and have the same problem. No water for 10 minutes. This issue has only occurred after we had to increase the pressure on the Glow Worm boiler. Not sure if it related or just a sheer coincidence.

 

[chris watkins]

Hi Chris, the system was spec'd and installed when we had the flat refurbished last year June. I'm really regretting not going the Megaflow route.

We've put only the mixer tap on hot water this morning and have the same problem. No water for 10 minutes. This issue has only occurred after we had to increase the pressure on the Glow Worm boiler. Not sure if it related or just a sheer coincidence.

Not related as two different systems. (unless the temp has increased as well)

You could post some photos of the cylinder / pump we may be able to suggest some pipe alterations that might help with the air entrapment which is what it sounds like but as before it is always likely to be a problem as you will have to start the pump before turning on the cold at any mixer.

 

[SuperDario]

Here is the video I have of the issue when the water does flow. I will post pics of the cylinder and pump too.

[video]https://drive.google.com/file/d/0B5mN1tpOTGMBcUlTbHFrWnpfZms/view?usp=sharing[/video]

 

[chris watkins]

The pump is "hunting" i.e. restriction on the inlet side.
Need to see pipework above.

 

[SuperDario]

Here are photos of the pipework around the pump and cylinder:

https://drive.google.com/folderview?id=0B5mN1tpOTGMBeGFJTHFtTVJtcEk&usp=sharing

 

[chris watkins]

No air free connection from cylinder, air then building up in outlet pipework over night.

Could try a Surrey or Warix flange, check water temp is no more than 60degC

PS please insulate the pipe work.

 

[Kay101]

I cannot see the photos but Chris is right, potentially a few issues
Negative pressure pump would start easier
Does it have a separate connection from the cylinder? I'm guessing not. It may be drawing in air when you use other outlets depending on how it is piped
Do the mixer taps have non return valves?
You need to make sure the pipes cannot be starved of water, this is happening somehow, usually piped up incorrectly, checked the instructions?

 

[SuperDario]

Thanks for the help guys. Used a Warix flange and it has substantially reduced the wait for hot water and for the pump to fire up. Gone from waiting up to 15 minutes to approximately 8 seconds.

Thanks for the assistance!

 

[plumbersm8]

Hi

The positive head pump which you have installed relies on a flow rate- if it is being supplied to mixer taps then it may struggle to activate ( they normally need about 1 litre of water in 30 secs to activate) a negative head pump such as the CTforcesu would be the better option as it activates on a presssure drop rather than a flow rate

 

[SuperDario]

Thanks plumbersm8! We started getting the issue again, although not as severe and I have purchased a 2.0 bar single CT FORCE 20 SU as well as a second coffin cold water tank for the loft. Hoping this should sort it out for good.

 

[Plumbstar Tom]

Yep, should likes a combination of air in the system, which has now been sorted, and not enough flow to activate the flow switches.

Coffin tank should sort that as it seems to be right on the limit of the minimum flow